Atomic Beam Experiment Research Articles

Large solid angle Lyman-α detector

A large solid angle Lyman-α (121.5 nm) detector designed for atomic beam experiments is described. The detector consists of 6 NO photoionization chambers which surround the beam and provide an average detection efficiency for Lyman-α photons of approximately 20% over the 3.5 cm length of the detector.

Laser optical spectroscopy on franciumD2resonance line

A highly sensitive method of detection coupled with a laser atomic beam experiment using on-line-produced Fr isotopes, has permitted finding and measuring the first optical resonance line of this element and its wavelength: $\ensuremath{\lambda}=717.97\ifmmode\pm\else\textpm\fi{}0.01$ nm. A high-resolution optical study has been undertaken, which has led to the determination of the hyperfine structure and isotope shifts for isotopes of mass number 208 to 213.

Energy dependence of the total cross sections for K(42Pj1m1to 42Pj2m2)+He collisions

The energy dependence of the total cross sections for the j1m1 to j2m2 transitions in the 42P state of potassium induced by collisions with ground-state helium have been calculated using a quantum-mechanical theory. The calculations have been carried out using the pseudopotentials of Baylis (1973) and those of Pascale and Vandeplanque (1974), for the energy range from 0.00716 to 1 eV. The cross sections relevant to crossed atomic-beam experiments and to cell-type experiments are calculated and discussed, the latter being averaged over a Maxwell-Boltzmann distribution of velocities for comparison with experimental results (the temperature range investigated is from 100 to 2500K). Emphasis is placed on the importance of knowing the photon excitation (polarisation, geometry of the system) accurately in order to interpret the data of atomic-beam experiments correctly.

Anomalous resonance-radiation pressure on an inverted atomic transition

We point out that the radiation force acting force acting on an atom due to resonant interaction with a plane traveling electromagnetic wave is opposite to the direction of propagation of the wave when there is a population inversion on the resonant transition. The effect can be used as a test for population inversion in an atomic-beam experiment.

The role of the Pauli principle in metastability exchange collisions

In optical pumping experiments, metastability exchange collisions are used to transfer orientation, alignment, ... between different atomic levels. This article studies the effect of such collisions on the atom internal variables density operator by a method used in a previous publication for spin exchange collisions. The calculations are valid when the nuclei of the two atoms are distinguishable as well as when they are identical particles, which allows a detailed discussion of nuclear identity effects (apparent magnetic field, etc...). Two cases are successively studied : no depolarization of the electronic angular momentum (He*-He collisions) and partial depolarization (Ne*-Ne collisions for example). The nuclear identity effects should be observable in low temperature optical pumping experiments with noble gases. In an Appendix, another particle identity effect is studied, which can be observed in atomic beam experiments : during the collision of two 3He atoms, both in the ground state, the spin state of the atoms scattered in a particular direction can be changed by nuclear indistinguishability effects.

Superpermeability of solid membranes and gas evacuation Part II Permeation of hydrogen through a palladium membrane under different gas and membrane boundary conditions

The permeation of atomized hydrogen through palladium membranes has been studied in view of its application for hydrogen pumping and recuperation. The atom permeation probability for a single impact with a membrane is measured by an atomic beam experiment in high vacuum and is found to be 0.1–0.2 practically independent of atomic hydrogen pressure, membrane thickness, temperature and boundary conditions in the wide ranges investigated. Thus, the membrane appears to be only a few times less permeable for atomic hydrogen than an opening in a thin wall and so a very large rate of hydrogen evacuation can be achieved. This is true in particular for ‘non-active’ palladium membranes, which have low permeability for molecular hydrogen and consequently can compress the gas by a factor of some orders of magnitude. Experimental results agree with the theory considered in Part I * of the present paper. Two † variants of pump construction are described capable of hydrogen evacuation followed by purification, compression and recuperation if required. The operation of these pumps is studied under different conditions. Both pumps described include the incandescent filament as a hydrogen atomizer, whose capacity limits the pumping speed. The utilization of the developed effect seems, however, to be most promising in cases where atomization is available by itself, for example, in thermonuclear fusion reactors.

Quantum interference effects in two-photon spectroscopy

Interaction of atoms with two intense coherent time-delayed short pulsed standing waves produces quantum interference effects in the atomic fluorescence. This type of quantum interference effect applied to Doppler-free two-photon spectroscopy (an extension of the Ramsey method of separated r.f. or microwave fields in atomic beam experiments) offers a number of important improvements in the presently available techniques of ultra-high-resolution spectroscopy of atoms, molecules, and crystals.

A determination of the NaAr ground state potential from differential cross section measurements

The differential cross sections for the interaction of Na with Ar has been measured in an atomic beam experiment at thermal collision energies. The data yield 0.85 × 10 −14 erg for the well depth and 5.05 × 10 −8 cm for the equilibrium distance. The result is compared with experimental and calculated results given previously.

Corrections to microwave atomic-beam experiments due to standing waves

Theoretical expressions are given, which allow microwave atomic-beam resonance experiments to be corrected for standing waves in the interaction region. Formulae are represented for the cases of the microwave direction being parallel, anti-parallel and perpendicular to the atomic beam.

Quantum transitions without quantum jumps

It is now recognized that quantum systems undergoing an uninterrupted transition between two stationary states (due to the influence of a coherent perturbation) do so in a smooth, continuous process that does not involve a quantum jump. The theoretical reasons for this continuity are given, and an atomic beam experiment is described that might be used to illustrate the process.

Arc-heated high-intensity source of hydrogen atoms

A very intense source of hydrogen atoms for atomic and molecular beam experiments has been obtained using pure hydrogen gas. In this work, a source head heated by a dc arc, very similar to the unit described by Knuth’s group [Rev. Sci. Instrum. 40, 1346 (1969)] was used. Fluxes of at least 4×1017 hydrogen atoms/sr sec with energies of about 5 eV have been repeatedly attained.

Raising the precision in measuring the fine-structure constant in an atomic beam experiment

The analysis of the ..cap alpha.. determination methods (..cap alpha.. = the fine structure constant) leads to the conclusion that the error in determining the fine structure constant can be reduced to 1 x 10/sup -6/. Moreover, it follows that the voltage drop across the tunnel barrier is measured with an error which depends on ..delta cap alpha../..cap alpha.. and does not exceed 5 x 10/sup -7/.

Zero-field hyperfine structure measurements of the metastable states 3d 2 4s 4 F 3/2, 9/2 of45Sc using laser-fluorescence atomic-beam-magnetic-resonance technique

In an atomic beam experiment we measured the hyperfine structure (hfs) of the metastable states 3d 2 4s 4 F 3/2,9/2 of Scandium, which were populated by electron impact. A single mode cw dye laser was used to create a population difference between neighbouring hfs states by optical pumping. Rf transitions between these states, equalizing the population numbers, could then be detected by repeating the optical pumping experiment and looking for the laser induced fluorescent light. The following constants of the magnetic dipole and electric quadrupole interactions have been obtained by this method:A 3/2=−158.513(3)MHzB 3/2=−5.19(2)MHzA 9/2=285.967(9)MHzB 9/2=−15.46(70)MHz From these constants and the corresponding values forJ=5/2, 7/2, as measured by [1], the following parameters can be calculated: 〈r −3〉 01 =0.911(4)a 0 −3 〈r −3〉 12 =2.395 (62)a 0 −3 and:α=〈r −3〉 01 /〈r −3〉 12 =0.38(1).

Atomic beam measurement of the lifetime of the3 P 1 metastable states of Mg and Ca

The lifetime of the metastable level3P1 of Mg and Ca have been measured in an atomic beam experiment. We excite the atoms to the3P1 state by electron collisions and we measure the decay length of the light emitted by the beam. The velocity distribution of the atoms is also measured by a time-of-flight technique. The decay length and the velocity measurements are then combined to compute the required lifetimes. The results are (2.4±0.2)×10−3 sec for Mg and (0.55±0.04)×10−3 sec for Ca.

Electronic excitation in collisions of H andH+withO2

The 115-750-nm radiation produced in collisions of 1.5-25-keV ${\mathrm{H}}^{+}$ and H with ${\mathrm{O}}_{2}$ has been studied in an atomic-beam experiment under thin-target conditions. For both ion and neutral impact, the ($b^{4}\ensuremath{\Sigma}_{g}^{\ensuremath{-}}\ensuremath{-}a^{4}\ensuremath{\Pi}_{u}$) first-negative ($1N$) and ($A^{2}\ensuremath{\Pi}_{u}\ensuremath{-}X^{2}\ensuremath{\Sigma}_{g}^{+}$) second-negative ($2N$) band systems of ${\mathrm{O}}_{2}^{+}$ are the most intense spectral features. Also observed are several emissions from excited states of O and ${\mathrm{O}}^{+}$. Relative cross sections for individual bands of the ${\mathrm{O}}_{2}^{+}$ $1N$ system, obtained by deconvolution of overlapped features in several vibrational sequences, were used to show that the vibrational population $P({v}^{\ensuremath{'}})$ for ${\mathrm{O}}_{2}^{+}$ $b^{4}\ensuremath{\Sigma}_{g}^{\ensuremath{-}}$ formed in both ${\mathrm{H}}^{+}$ and H impact is in good agreement with the predictions of a simple Franck-Condon mechanism over the 2-25-keV energy range. Total cross sections for formation of ${\mathrm{O}}_{2}^{+}$ $b^{4}\ensuremath{\Sigma}_{g}^{\ensuremath{-}}$ in ${\mathrm{H}}^{+}$ and H impact, determined from the latter results by normalization to previous proton-impact data, are in good agreement with values calculated via application of the semiempirical procedure developed recently by Edgar et al. For both projectiles the semiempirical approach gives a good prediction of the energy dependence and an adequate prediction of the magnitude of the cross sections for formation of ${\mathrm{O}}_{2}^{+}$ $A^{2}\ensuremath{\Pi}_{u}$ determined by integration of measured $2N$ band intensities.

Nuclear hexadecapole shielding factor for the holmium atom

The nuclear hexadecapole shielding factor ${R}_{H}$ for the $4f$ electrons of the holmium atom ($Z=67$) has been obtained. This calculation was carried out in connection with a recent atomic-beam experiment of Dankwort, Ferch, and Penselin, which indicates the presence of a nuclear hexadecapole interaction with the $4f$ electron, leading to a value of the nuclear hexadecapole moment $H({\mathrm{Ho}}^{165})=0.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}48}$ ${\mathrm{cm}}^{4}$. This result has to be corrected for shielding or antishielding effects of the holmium atomic core electrons on the $4f$ electron, which experiences the interaction with the nucleus. The present paper gives the procedure and the results of the calculation of ${R}_{H}$, which was found to be + 0.24 (shielding). Thus the value of the moment $H({\mathrm{Ho}}^{165})$ obtained by Dankwort et al. should be multiplied by the factor $\frac{1}{(1\ensuremath{-}{R}_{H})}=\frac{1}{0.76}$, giving a corrected value $H{({\mathrm{Ho}}^{165})}_{\mathrm{corr}}=1.06\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}48}$ ${\mathrm{cm}}^{4}$.

Formation of electronically excited CO2+ in collisions of H+, H, He+, and Ne+ with CO2

Electronic excitation in collisions of 200 eV–25 keV H+, H, He+ and Ne+ with CO2 has been investigated under single-collision conditions in an atomic beam experiment. For each of these projectiles, the B 2Σu+ and A2πu states of CO2+ are the dominant electronically excited species emitting in the 200–500 nm wavelength range owing to target excitation. Although dissociative electron capture by He+ and Ne+ to form electronically excited CO+ minimizes the energy defect, no emission is observed from CO+ A2π, and formation of CO+B2Σ+ is of only minor importance. The latter observations are in direct contradiction to predictions derived from the adiabatic criterion and demonstrate that, in the competition among allowed excitation processes, details of the electronic structure of the collision partners override energy considerations. The qualitative features of the emission spectrum excited by H+, H, and He+ are insensitive to relative velocity over the energy range covered. The ratio of the cross sections for excitation of CO2+ B−X and A−X emissions is about 0.20 for H+ and 0.40 for He+. In Ne+ impact, the CO2+ A state vibrational distribution changes significantly, the (B−X)/A−X) cross section ratio decreases from 0.46 to 0.07, and the relative importance of Ne and Ne+ emissions diminishes markedly as the energy is reduced from 4 keV to 200 eV. Our results are compared with those for electronic excitation produced by photoionization, electron impact, and Penning ionization of CO2.

107Ag and 109Ag Nuclear Magnetic Resonance Studies of Ag+ Ions in Aqueous Solutions

The NMR lines of 107Ag and 109Ag have been investigated in aqueous solutions of AgF, AgNO3, and AgClO4. The ratio of the Larmor frequencies of 109Ag and 107Ag has been measured in various samples: ν(109Ag)/ν(107Ag) = 1.149 639 7 (8). No primary isotopic effect was to be detected within these limits of error (0.7 ppm). This ratio yields the hyperfine structure anomaly 107⊿109 = − 0.004127 7(7). The concentration dependence of the chemical shift of the 107Ag and 109Ag resonance frequencies was determined. Using this dependence, the ratios of the Larmor frequencies of the 107Ag and 109Ag nuclei for infinite dilution relative to the resonance frequency of 73Ge in GeCl4 are given. The magnetic moments of the 107Ag+ and 109Ag+ ions merely surrounded by water molecules are μ(107Ag+) = − 0.113 045 3(9) μN and μ(109Ag+) = − 0.129 961 5(10) μN without diamagnetic corrections. These values are compared with the result of an atomic beam experiment, the difference of the moments is due to the shielding of the silver nuclei by water molecules around the ions. The shielding constant is σ* (Ag+ in H2O vs. Ag atom) = − 0.000 94(17). Preliminary values of the relaxation times are given.

Two and Four Quadrant Gating Circuits for Crossed Atomic Beam Experiments

Descriptions are given of two circuits which generate scaler gating pulses and beam modulating pulses as required for crossed atomic beam experiments. For the case when only one of the crossed beams is modulated, a circuit is described in which a sinusoidal-type signal is filtered by a tuned amplifier whose gain is 2000 and Q value is 260, and then passes through a level crossing detector, a frequency doubler, and several variable delays to produce two complementary square wave pulses. When both atomic beams are modulated, a second circuit produces a scaler gating pulse from each of the quadrants of the modulating period. Several combinations of variable delays permit variable phase differences between each of the four gating pulses. Circuit stability is better than 0.01%.

Atomic-beam deflection and broadening by recoils due to photon absorption or emission

An atomic-beam experiment, based on momentum transfer between photons and atoms during resonant interaction, is described. Curves providing the first direct experimental evidence in the optical region of the isotropic recoil effect in spontaneous emission, have been obtained. Other curves show the possibility of deflecting an atomic beam with sufficient efficiency to give a new method of detection of optical resonance. Some spectroscopic applications, also valid for atoms with a diamagnetic ground state, are considered.